Cosby's Fatherhood and Time Flies remain popular and his new book may exceed even their sales. Once past the introduction by Dr. Alvin F. Toussaint--an unrequired nihil obstat to the contents--the reader will revel in Cosby's tender, ruefully funny recollections of amatory hits and misses. Beguiling in the manner of the entertainer who laughs mostly at himself, the anecdotes contrast his growing years in Philadelphia, where he was born in 1937, with today. Unlike a modern boy of 10, ``transported by the ballad `I Want Your Sex!' '' the author writes, his own youth might have been lived in medieval days. A teenager when he felt the first erotic stirrings, Cosby confesses fumbling attempts on nubile girls and vying for stud status with bragging pals. He makes his joy palpable when he tells about meeting Camille Hanks, who became his wife 25 years ago, the woman who verifies to him that love and marriage go together, regardless of imperfections. 850,000 first printing; first serial to Good Housekeeping; Doubleday Book Club main selection; Literary Guild featured alternate; paperback rights to Bantam. (May)